Tracy Romano, the aquarium's executive vice president of research and zoological operations, says Naku had battled the illness since last fall. Aquarium officials are working with University of Connecticut experts in performing a necropsy on the beluga, which had been part of the aquarium's collection for three decades.

The aquarium's beluga whales have been a popular attraction for years, occupying three connected pools with more than 750,000 gallons of water in the Arctic Coast exhibit.